PROJECT SUMMARY/ABSTRACT Exposure to automobile exhaust and wastes generated by industrial combustion through contaminated air is one of the most common environmental exposures among the general public, and long-term exposure to such polluted air and its main constituent, fine and ultrafine particulate matter (PM), has long been recognized as a major risk factor for cardiovascular morbidity and mortality. Notably, recent population-based epidemiological studies identify PM's significant influence on cognitive function in humans, and indicate it as an increased risk for developing Alzheimer's disease (AD). These findings suggest that exposure to PM causes lifelong impact on the central nervous system and substantial neurotoxicity, giving rise to accelerated cognitive decline and possibly the development of AD neuropathology. However, research has yet to fully elucidate the biological mechanisms of PM-induced neurotoxicity, at the molecular and cellular levels, or to elucidate functional, morphological, anatomical, and/or pathological changes leading to cognitive decline and increased risk for AD. Given our expertise and recently emerging evidence in the field, we hypothesize that the exposure to PM perturbs dendritic spines and promotes the buildup of toxic amyloid-beta (A?) species by aggravated microglial activation and neuroinflammation. The proposed research will rigorously assess the changes in dendritic spine morphology, A? buildup, microglial activation, and inflammatory profiles in mice exposed to environmentally- relevant PM and determine the microglia's prime role in PM-induced neurotoxicity by ablating them. The proposed project is significant as we aim to identify microglia as a key mediator of inhaled PM-induced neurotoxicity and reveal inhaled PM's biological impact on cognitive decline and the risk for AD. Deciphering cellular cascades triggered by exposure to environmental PM will exhibit highly intrinsic merit toward understanding the environmental impact on brain health and will contribute to improving public awareness of the risk of exposure to environmental contaminants. This project has significant translational value, as an improved understanding of the biological mechanisms by which exposure to PM influences cognitive decline will pave the way for more effective preventive and therapeutic measures.